1. Field of the Invention
The present invention relates to the manufacture of metal containers, such as cans, that are coated with a polymer “washcoat” coating. More particularly, the present invention relates to the removal of water from a mixture of washcoat and residual water that may be formed during the manufacture of such containers.
2. Background of the Invention
“Two-piece” containers, which are common in the production of food and beverage cans, are manufactured through a drawing and ironing (“D&I”) process using suitable metal cups to form a cylindrical body and base (sometimes referred to as the “shell”) as a single first piece, with a lid constituting a second piece. Another type of can, a “three-piece” can, is manufactured from a cylindrical piece and two end pieces.
The metal cups and the dies that are used in the D&I operation of a two-piece can manufacturing process typically utilize a lubricant, such as oil, to facilitate that operation. During the drawing operation, however, the lubricant often comes in contact with surfaces of the can and subsequently remains adhered thereto. Therefore, cans are typically washed with an acid or caustic material to remove any such lubricant prior to application of a protective coating layer. Following this wash, the can is typically rinsed with water, sometimes in several rinse stages. Once rinsed, a coating termed a “washcoat” (defined below) is typically applied to the can.
Following the rinse step, however, residual water or other contaminants may be in contact with surfaces of the can. In addition to coating the cans, therefore, the washcoat operation may also incidentally remove contaminants as well. In a typical system for applying a washcoat coating, cans pass through a curtain of the washcoat. Washcoat that does not adhere to the exterior surface of the can may carry residual water, or other contaminants, with it and be recirculated for future use.
The residual water that is carried with the washcoat, however, dilutes the washcoat, thereby potentially leading to poor or low film weight control and, as a result, inadequate performance. In some situations, the addition of concentrated washcoat to correct the over dilution is impractical or undesirable. In such cases, for example, it would be desirable to remove over diluted material from the system to make room for concentrated washcoat so that proper washcoat film weights can be achieved.
Accordingly, there is a need for a method of removing residual water from washcoat.